1. Field of the Invention
The present invention relates to a radio module having an antenna and, more particularly, to a radio module installed in a radio communication terminal such as a cellular phone, PDA (Personal Digital Assistants), cordless phone, or transceiver which is used in contact with or close to a user.
2. Description of the Related Art
Recently, in a mobile communication terminal represented by a cellular phone, a built-in antenna accommodated in a housing is mainly used. However, since such built-in antenna is arranged close to the ground pattern of a circuit board accommodated in the housing, the impedance and bandwidth obviously decrease. Also, when using a monopole antenna, a radiation pattern varies in accordance with the size of the ground pattern of the circuit board, thus posing a problem.
In order to improve the radiation pattern of an antenna, an arrangement has been proposed (e.g., see Jpn. Pat. Appln. KOKAI Publication No. 2000-40910) in which, e.g., an L-shaped long plate with one end connected to the ground surface of a circuit board is located on this ground surface, and a current flowing to the ground pattern of the circuit board is reduced by using this plate, thereby reducing degradation of directivity characteristics.
However, as is apparent from FIGS. 1 to 4 in Jpn. Pat. Appln. KOKAI Publication No. 2000-40910, in the conventionally proposed arrangement, the L-shaped plate is located on a circuit board surface close to a user's head. Accordingly, since the L-shaped plate is also close to the user's head, this module tends to be influenced by the user, and the improvement effect of the radiation characteristics of the antenna decreases. On the circuit board surface facing the user, a key pad and various circuit components are mounted at high density. Hence, when the L-shaped plate is located on the circuit board surface facing the user, the circuit board must become large, and this leads to an increase in size and cost of the terminal.